The present invention relates to a combined spring-and-shock-absorber system for supporting wheel suspensions or axles on a vehicle body using a tubular roll bellows (U-bellows) arranged between a wheel-bearing or wheel-controlling connection and a connection on the vehicle body side, the bellows being arranged between an outer bell and a rolling piston, the outer bell and the rolling piston, in each case, having at least partially varying diameters over the height of the corresponding component, and having walls that contact the tubular roll bellows. Both ends of the tubular roll bellows are sealingly secured on the rolling piston at segments having different diameters, the lower mounting section having a larger diameter than the upper mounting section.
U.S. Pat. No. 4,518,154, describes a conventional pneumatic suspension system for vehicles. The outer bell and the multi-part rolling piston enclose a unitary differential roll bellows. Due to the low gas pressure and the use of a differential roll bellows, this design may require an installation space of an excessively large volume.
In addition, German Published Patent No. 297 02 927 describes a conventional spring-and-shock-absorber system, which is composed of a displacement device without a bellows, a hydraulic accumulator, and a hydraulic line connecting these parts. In the hydraulic line, a mechanical choker valve is arranged. The displacement device, as is conventional in a hydropneumatic suspension system, connects the vehicle wheel suspension to the vehicle body. The system is filled with a hydraulic fluid. The latter, when a vehicle wheel is spring deflected, is forced through the choker valve into a hydraulic accumulator. The flow resistance of the choker valve generates a damping force, whereas the compression of the gas volume in the hydraulic accumulator creates a spring force. In accordance with the principle of displacement presented here, a displacement piston plunges into a displacement cylinder. Both parts move in a guiding and sealing interaction, generating friction against each other. The friction impairs the response time of the spring-and-shock-absorber system, so that when it is used in a vehicle, the driving comfort of wheels supported by this system may not be optimal.
U.S. Pat. No. 4,493,481 depicts a pneumatic spring for motor vehicles having a closed spring volume and two effective, changeable spring surfaces, whose sizes are a function of the spring elongation, and which are supported in a coaxial manner against each other, the spring surfaces being of different sizes, mutually acted upon by pressure, and facing away from each other. The tubular roll bellows is secured on both ends, having the same diameters, on the rolling piston and is configured as a one-piece tubular roll bellows.
In British Published Patent No. 2,318,851, a multi-bellows spring system having hydraulic accumulators connected by lines is described. Two separate, enclosed bellows, that are different in size, have each available to it its own hydraulic accumulator. These are two systems that are separated from each other hydraulically, each bellows, viewed in the spring direction, on the chassis side and on the wheel-controlling side, having the same piston surfaces. The bellows are essentially freestanding bellows, whereas in the exemplary embodiments according to the invention, the bellows are supported over virtually the entire area between an outer bell and a rolling piston. Between the bellows, there is a mechanical transmission element that is independent of the bellows.
As described in numerous publications and from practice, conventional diverse motor vehicle air suspension systems are essentially composed of a roll bellows that encloses a volume of air and that is bordered on its one end by a chassis-fixed covering plate and on its other end by a wheel-side rolling piston. Conventional air spring systems of this type may lack stability with regard to tilting, so that additional measures may be required for the longitudinal and transverse guiding functions.
The present invention concerns the development of a combined spring-and-shock-absorber system, which contains a low-friction, thin-design displacement device that is based on a tubular roll bellows and that has great transverse rigidity. In addition, an objective of the present invention may include creating a suspension device that is acted upon by a pressure medium, the device being controllable with regard to suspension performance and the height of the spring, and it being such that it is completely or at least substantially possible to do without external longitudinal and transverse suspension links.
According to one exemplary embodiment and/or exemplary method of the present invention, a tubular roll bellows may he used, which may be configured as a differential roll bellows, whose interior may be filled with a fluid and may communicate to a hydraulic accumulator that is supported on the chassis or on the vehicle side.
The type of displacement bellows, the type of connection on the chassis and on the vehicle body, and the possibility that the bellows interior may be filled with a fluid that is prestressed using a gas make possible a slim displacement device that does not have a mechanical, friction-producing longitudinal guide element. A separate longitudinal guide element may be superfluous because the pressure in the displacement bellows, as a result of the two bellows meniscuses, centers and stabilizes the shock-absorber leg parts, which move relative to each other.
In response to a pressurizing or depressurizing of the displacement device, a hydraulic fluid flows back and forth between the displacement device and the hydraulic accumulator via a narrowing of the cross-section in the form of a hydraulic line or an opening. The configuration of the line, or the opening, and the characteristics of the restrictors arranged there influence the system dampening in accordance with the size and shape of the opening cross-section. In this context, the individual restrictor may be configured either as a nozzle or an aperture, or at least as a one-way restrictor. When one-way restrictors are used, at least one valve for each flow direction may be arranged in the cross-section of the line, or the opening.
The gas cushion of the hydraulic accumulator normally constitutes the suspension system.
As a result of using a tubular roll bellows in the form of a differential roll bellows, the mechanical friction of the entire system may be essentially reduced to the interior friction of the bellows or membrane material. As a result, the spring-and-shock-absorber system may demonstrate virtually ideal responsiveness over the entire range of damping rates. The outer bell and/or the rolling piston may each be directly securedxe2x80x94even without the interposition of rubber-elastic elementsxe2x80x94on the vehicle body, or on the chassis, via flexible couplings. This may reduce, inter alia, the component weight, the manufacturing costs, the difficulty of assembly, and maintenance costs.
Both rolling piston halves, in addition to the two corresponding halves of the differential roll bellows in the suspension device according to the present invention, provide a self-centering guide function between the double rolling piston and the outer bell. On account of the relatively high operating pressurexe2x80x94in comparison to conventional air suspension systemsxe2x80x94this radial guidance may be especially stable.
On the other hand, due to the rubber-elastic decoupling of piston and outer bell, the excitation of higher-frequency vibrations may be filtered out. The shape of the suspension device as a differential roll bellows may be oblong, which, in addition to the very good radial (lateral) guidance, also provides very good longitudinal guidance. For this reason, it is possible, substantially or even entirely, to dispense with a separate longitudinal and transverse control arm.
The spring force is determined by the difference in the effective radii of curvature of the two roll bellows halves (differential roll bellows halves). The radii of curvature of the roll bellows halves are produced by the differences in the radii (or diameters) of the outer bell and the two piston (halves). If the difference between the individual piston radii is slight, then the difference in the radii of curvature of the roll bellows halves may also be slight. This has the consequence that it is possible to operate at a high operating pressure, as may be required in active chassis control systems.
The difference in the effective roll-bellows radii of curvature, instead of using a difference in the piston radii, may be realized using a radius difference of the effective outer-bell segments.
The roll bellows halves, arranged so as to be opposite each other, are clamped, on one side, to the outer bell and, on the other side, to the piston using clamping rings so as to be fixed in a mechanically reliable fashion and tight in the pneumatic/hydraulic sense.
The filling of the spring and the control system, specifically setting the spring level, but also controlling the rolling motion, may be carried out using a controlled pressure pump, which may be connected to the tubular connectors located on the outer bell. In addition, an accumulator volume may also be connected.
For receiving a shock absorber, the piston may be configured so as to be a hollow cylinder. In this manner, it is possible to do without a separately arranged shock absorber. This may save both additional installation space as well as additional assembly work. The shock absorber, surrounded by the spring sleeve, may be protected from road impurities.
The spring volume of the roll bellows halves may alternatively be filled with a compressed gas (such as, for example, air) or with a hydraulic fluid.